Aircraft heating control system



March 9, 1948. w. J. FIELD AIRCRAFT HEATING CONTROL SYSTEM Filed Jan. 31, 1944 Junentor WILLIHM tI f/E'LD attorney Patented Mar. 9, 1948 AIRCRAFT HEATING CONTROL SYSTEM William J. Field, Minneapolis, Minn., aslignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January 31, 19, Serial No. 520.439

18 Claims.

This invention relates to the field of aeronautics and more particularly to a solution of the problem created by the accretion of ice on airfoil surfaces during flight.

During flight, the formation of ice on an aircraft results from the freezing of water droplets which are intercepted by the leading edges and exposed surfaces. supercooled water droplets exist in a majority of clouds when the temperature of the cloud is below 32 F. While there is a tendency towards the formation of ice-crystal clouds rather than water clouds, as the temperature decreases below the freezing point, water clouds can none the less be cooled to very low temperatures, and have been found even at -60 F. in the polar region.

Water in the liquid form at temperatures below freezing exists in a very unstable state and when disturbed is rapidly changed, at least partially, into ice. The impact of the droplet with various parts of the airplane is the disturbing influence which begins the freezing process.

The formation of ice on airfoil surfaces causes loss of lift by deformation of the airfoil section by the ice which is frozen on the leading edges. Under these conditions, the plane stalls at air speeds well above the normal stalling point. Formation of ice on airfoil surfaces also increases the drag, particularly when rough ice forms back of the leading edges and on various protuberances. A third undesirable effect brought about by accretion of ice is increase in the weight of the craft. It will be seen that the cumulative eflect of these three factors may be of very serious consequence to the operation of the craft.

The rate of ice accretion has been found to depend upon a combination of a large number of factors, but principally upon the air speed, size of the cloud or rain droplets, their density in the atmosphere, and the shape of the external area of the airfoil surface. The rate of ice ac cumuiation varies over wide ranges and may be less than one half an inch in one hour or over one inch in one minute. Cases have been reported where craft without deicing equipment have been forced down out of control after less than five minutes of flight through an icing region.

It is the purpose of this invention to provide a system for deieing aircraft wings and so forth which is peculiarly adapted to the unusual demands and conditions of this type of service. It is also an object of my invention to provide an aircraft heater including a combined heat generator and exchanger together with a control system particularly adapted to aircraft applications.

It is another object of my invention to provide an aircraft wing heating system in which the amount of heat delivered to the wing generally varies with the air speed-of the craft, and thus with the heat loss.

It is a further object of my invention to provide, in an aircraft wing heating system having a burner whose heat output varies with the speed of the craft, means for preventing the flame of the burner from being extinguished due to speed of the craft in excess of the range to which the heater is adapted.

Further objects and advantages of my invention are set forth in the following description, taken with the accompanying drawings. and the novel features thereof are pointed out in the appended claims. The disclosure, however, is illustrative only, and I may make changes in detail, especially in matters of shape. size and arrangement of parts within the principle of the invention, to the full extent indicated by the broad general meanings of the terms in which the appended claims are expressed.

In the drawing.

Figure 1 is a schematic showing of a wing deicing system embodying my invention, and

Figure 2 is a modification of the system shown in Figure 1.

Referring now to Figure 1 of the drawing, my wing deicing system is seen to comprise generally a temperature responsive member III consisting of a resistance element having a substantial positive temperature coefficient of resistance, mounted in heat conductive relationship with an airfoil ll subject to accretion of ice, and arranged to influence the balance condition of an electric bridge if by its change in resistance with change in the ambient temperature. As a result of un' balance of bridge ii, a signal potential is impressed upon an amplifier l3 whose output selectively energizes one of a pair of relays generally indicated at it for initiating operation of a motor I! in either a forward or a reverse direction. Operation of motor I5 is effective through a mechanical connection l8 to adjust the heat output of a heater means generally indicated at It so that on an increase in temperature of the airfoil surface the flow of air through the heater means is decreased. while on a decrease in temperature of the airfoil surface the flow of air through the heater means is increased. Operation of the motor at the same time acts through a link it upon a variable resistance member H to tend to rebalance the bridge; balancing of the bridge removes the signal potential from the amplifier,

deenergizing the relays and therefore interrupting operation of the motor.

As more fully pointed out hereafter. heater means Ii depends for its operation on the flow of air therethrough, but if an excessive flow of air takes place the ilame of the heater means is apt to be blown out. while if the air flows through the heater means at an unduly low rate. the ilame is erratic and again may go out. A responsive means is therefore provided and is electrically associated with bridge l2 so that. when the flow 0! air through the heater means increases or decreases in magnitude beyond predetermined limits. the bridge circuit is again unbalanced. independently of the response of temperature responsive member ll. in such a direction as to restrict the flow of air through the heater means. The structure of my system will now be considered in greater detail.

It will be seen that airfoil II is provided with an aperture 2| in its leading edge and that a conduit 22 is provided to conduct air entering through the aperture II at a rate depending on the velocity of the airfoil through the air. so that it passes through a heat exchange portion 23 of the heater means in a first direction and is thereafter conducted by a conduit 2| into a manifold 25. Maniiold 25 passes longitudinally along the airfoil in the neighborhood oi its leading edge, and is provided with a series of apertures whereby the heated air flowing therethrough is directed against the inner surface of the leading edge of the airfoil to raise its temperature. A suitable means, such as aperture 28 in the trailing edge of the airfoil. is provided for the escape of the air after it has given up its heat. A damper 21 is arranged in conduit 24 to restrict the passage of air therethrough.

Conduit 22 is iurther provided with a branch 30 which is adapted to conduct a portion of the air entering at aperture 2| through heater means it along an independent path which includes a combustion chamber 2! surrounding the passages of heat exchanger 23. Branch 30 is provided, near its point of junction with combustion chamber 29, with a Venturi member II which cooperates with a fuel supply nozzle 32 to provide a flow 0i combustible vapor to the combustion chamber. The products of combustion are conducted directly to the outside of the airfoil through a short conduit 83. and this conduit is provided with a second damper 34. The amount of fuel provided to the burner is dependent on the rate of flow of the air with respect to Venturi member 3|, and this rate oi flow in turn depends upon the speed of movement of the airfoil through the air; that is. upon the airspeed of the craft. It has been found, however, that if the how oi air passing Venturi member 3i exceeds a certain magnitude, the eflect is to extinguish the flame oi the burner rather than to increase its heat output. Similarly, if the flow of air passing Venturi member ill is of less than a certain magnitude. the flow of fuel to the burner is not regular. and erratic operation of the burner results.

The flow of air past Venturi member 3! may be determined by observing the pressure differential between the combustion chamber and conduit 22: a pressure difl'erential in excess of a determinable value is indicative of excessive how of air past Venturi member 3!, while similarly, a pressure differential which is less than a second determinable value is indicative of an inmfficient flow of air past venturi 8|. To determine the pressure diii'erential iust described, 1 provide a pair of bellows members 28 and I rigidly mounted on suitable support members ll and connected as by tubes 31 and ll with conduit 22 and combustion chamber 2! respectively. The free ends of bellows members I! and 3B are Joined as by a link ll ofsuch length that when there is no pressure diilerential both bellows are considerably compressed.

An arm ll. pivoted as at I5, is connected in a suitable fashion as at It with link 48, so that motion of link 42 to the left as seen in the figure causes arm 44 to rotate about its pivot in a counter-clockwise direction. Arm M is provided with an insulating portion 41, and the arm is also suitably insulated from its pivot. A pair of contact members ll and ii are arranged for electrical cooperation with arm ll. so that a predetermined displacement of the arm in a counter-cloclrwise direction will cause the arm to make electrical connection with contact 50. while a predetermined displacement of the arm in a clockwise direction will cause the arm to make electrical connection with contact 5|. Contacts ill and ii are electrically connected as by conductor 52 and are Joined to the bridge by conductor 53. and arm M is connected with the bridge by a conductor N, in a fashion now to be described.

Bridge I! is constructed along the general lines of the familiar Wheatstone bridge and comprises fixed resistors 60, BI, 62. 82, BI, and and variable resistors 88, 21, Ill. and I], having movable contacts 1 I. II, I2, and 19 respectively. Resistors B4 and III in series are connected in parallel with resistor l'l. so that the relative magnitude of the currents flowing in the series combination and in resistor l1. respectively, due to a potential difference across the parallel network may be varied. Electrical energy is provided to the bridge by a transformer 13 whose primary winding 14 is connected to a suitable supply of alternating current as by conductors l5 and I8 and whose secondary winding 11 is connected to the input terminals 80 and 8| of the bridge as by conductors 82 and 83.

A circuit may be traced around the bridge as follows: input terminal at, resistor 62. conductor 88, resistor 61, movable contact 18, conductor 88, resistor 03, conductor 98. resistor ll, conductors I99 and IN. resistor 65. conductor I09. input terminal 8i, conductor H2, resistance bulb l0, conductor H2, resistor 68. conductor iIB, resistor ill, conductor H8, resistor BI and back to input terminal 80. Movable contacts II and 12 of resistors 68 .and I1 comprise respectively the output terminals of the bridge: contact 12 is grounded as by conductor and terminals 81 and 93 of amplifier ii are grounded as by conductors 8i and 95.

For convenience, let the resistance in the circult between input terminal 80 and movable contact ll be of a magnitude A, that between terminal 80 and movable contact I2 of magnitude B, that between movable contact H and input terminal ll of magnitude C, and that between movable contact 12 and input terminal 8i of magnitude D. The balance condition of the bridge is that at which no potential diflerence exists between movable contacts I l and I2, and this condition obtains when A/B=C'/D. For any given setting of resistors 86, a1, and 10, there are only two variable resistors in the bridge, resistance bulb l0 and resistor ll. Since the resistance of resistance ill varies directly with changing 5 temperature. a decrease in due to a tall in temperature causes an unbalance in the bridge, which can only be rebalanced by a movement oi movable contact 12 to decrease D and increase B until the above equation again holds true.

Amplifier I8 is provided with alternating current through conductors I4 and It, and has input terminals 85 and II and output terminals 92, 93, and 94, terminal at being grounded. The amplifier may be of any suitable design, and is of such a type that an input signal of a first timephase relationship impressed upon input terminals B8 ard 81 is eiIective to produce an output signal across output terminals 92 and 93, while an input signal of the opposite time-phase relationship is adapted to produce an output signal across output terminals 84 and 93.

A pair of relays 98 and II, including circuit controlling members 98 and 80, have their windings Hill and NH connected in the output circuit or amplifier II by conductors Ill and III in such a fashion that the appearance oi an output signal across output terminals 92 and 03 is effective to energize the relay 98, while the appearance of an output signal across terminals 94 and 93 is efiective to energize the relay 91. The circuit between the relays and output terminal 98 is completed through a second ground connection I02 common to both relay windings.

Th operation of relays 96 and 91 is eflective to control the supply of alternating current from a suitable source supplied by conductors I03 and I M to motor It in such a fashion as to energize the motor for selective forward and reverse operation, depending on which 01' the relays is energized. To this end, conductor IN is connected to the circuit controller members of the relays, which control the flow of current to selected windings of the motor, while conductor llll is grounded as at I05: the windings of motor I! are suitably grounded as at I08.

Rotation oi the shaft of motor I! is transmitted to movable contact I2 through connection I9, and the second mechanical connection It transmits rotation of the motor shaft to dampers 21 and 34 by branches H0 and Ill. The mechanical arrangements are such that rotation of the motor in a direction tending to close the dampers acts also to move contact I! to the left as seen in the figure whereby to increase D and decrease B. The electrical connections between bridge l2, amplifier l3. relays I4, and motor II assure that the relay energized by amplifier [3 on an unbalance signal from the bridge, due to a decrease in C. initiates operation of motor II in a direction which opens the dampers and moves contact 12 to the right.

Before outlining the method in which the system functions, it should be pointed out that resistor BB is made adjustable to provide means for calibrating th bridge circuit. and that resistor 61 is made adjustable to provide means for varying the control point or the bridge circuit: resistor III is made adjustable to provide means for adiusting the diflerential response of the bridge circuit. It will be understood that it it is desired to construct a bridge to meet one specific set of conditions, none oi these resistors needs to be variable, but may be constructed to the exact value desired or in some cases omitted altogether, the resistive efiects being provided by other resistors forming a permanent part of the bridge.

It should also be pointed out that the effect 6 is to short out resistor II. and therefore Produce a marked unbalance in the bridge due to a decrease in B.

The function of my system will now be described. First let it be assumed that the craft or which airfoil ll iorms a part is in motion through the atmosphere at a speed within the range causing a pressure diflorential such that arm 44 makes contact neither with contact Ill nor with contact II, and that the temperature or the airfoil suri'aoe is well above that at which icing could occur. That being the case, the resistance at temperature responsive resistor It is such that the bridge is in balance at a position 01' contact I! along resistor l'l resulting from a rotated position of motor ll corresponding to complete closure of dampers 21 and Il. The bridge being in balance, contacts II and II are at the same potential and no signal is impressed across the input terminals of amplifier II. No output signal is transmitted to relays ll, and therefore motor It remains unenergiaed.

Now let it be assumed that the craft 01' which airfoil ll comprises a portion moves into an atmosphere whose temperature is falling. The resistance oi resistor It decreases in response to this change in temperature, unbalancing the bridge circuit by decreasing C: all other values of resistances in the bridge circuit remain as before. Decrease in the resistance oi resistance bulb It decreases the total resistance or that portion of the bridge including resistors II, II, it and Ill, and an increased current fiows therein. Now, although A has not changed, the current through A has increased, and therefore the voltage drop through A has increased; this voltage drop through E remains the same. Contacts ii and 12 are no longer at the same potential. but a voltage appears across them, the potential diflerence between contacts II and 12 having the same phase relation as that between terminals II and ill. This signal potential is impressed upon amplifier I 3 as by conductor Ill and ground connections and SI, and results in the appearance or an output potential between terminals 92 and 83. This potential is conducted to winding III! of relay 96 through ground connections 95 and It: and conductor H5, energizing relay it to complete a circuit providing alternating current to motor I! as follows: conductors I03. Ill, and III, circuit controlling member ll, conductor I20, motor l5, ground connections I" and I". and back to conductor I04. Completion of this circuit energizes motor It to rotate in such a direction as to open dampers 21 and SI, and to move contact 12 to the right along resistor 11. This movement oi. contact 12 increases B and decreases D in the equation given above. without changing the total resistance between terminal 80 through resistor II to terminal Bi. Thus although the current through 8 remains the same, 3 itself increases until the volt age drop through B is the same as that through A. When this condition prevails. contacts II and 12 are again at the same potential. no signal is impressed upon the input or the amplifier, and operation oi the motor is interrupted.

This rotation of motor ll, however, has at the same time rotated dampers 21 and it into partly open positions. and air flows through the venturi or the heater means, providing in the burner a combustible vapor and means for supporting the combustion. At the same time, suitable means. not shown, are actuated. in any conventional tashion, to ignite the combustible vapor now bein of contact between arm n and contact to or ll 76 provided in combustion chamber II. A suitable control system is operatively associated with the igniting means just referred to for detecting the absence of flame in the burner and actuating the igniting means, whenever the response or the bridge and the position of damper ll indicates the need or increase in temperature of the airfoil. It will readily become apparent that further drop in temperature results in further change in the resistance of resistor It in the same sense, and accordingly produces wider opening of dampers I1 and 34 and increased fuel consumption and therefore increased heat output by the heater means. This is true regardless of whether the further temperature decrease is due to passage of the craft into a cooler atmosphere or to increased conductive heat loss due to increased airspeed.

At the same time that damper 34 was opened to permit the generation of heat in the combustion chamber of the heater means, damper 21 was also opened allowing air to flow through the heat exchanger and to be warmed by heat exchange relation therewith. Further flow of this heated air through manifold 25 and impingement 0f the heated air with the interior of the airfoil near its leading edge act to give up heat to the airfoil, and if sufllcient volume of air at sufiiciently high temperature is thus discharged. the temperature of the surface begins to rise. Resistance bulb III is shown at a position relatively remote from the leading edge of the airfoil. where maximum icing occurs, but the relative propinquity of the bulb and the leading edge is a matter left at the discretion of the designer, since more or less heat lag between the leading edge and the bulb may in some cases be considered desir-able.

It must be understood that, so long as an accretion of ice overlies the airfoil. little increase in the airfoil temperature above 32 F. can occur. However, when a layer of ice next the airfoil is melted, vibration, gravity, and wind pressure combine to cause the ice to fall away from the airfoil, and after the remaining water evaporates the temperature of the airfoil rises rather rapidly at first, to a value depending on the temperature of the ambient air and the total area of the airfoil conducting heat therefrom. and also upon the air speed of the airfoil as it aflects the output of the heater means.

With a rise in temperature. the resistance C of bulb Iii increases, and with it the total resistance of that portion of the bridge including resistors BI, 60, 86, and HI, and a decreased current flows therein. Now although A has not changed, the current through A has decreased and therefore the voltage drop through A has decreased, the voltage drop through B remaining the same. Contacts II and 12 are no longer at the same potential, but a voltage appears across them, the potential difference between contacts II and 12 having the same phase relation as that between terminals Ill and BI. It is thus evident that the signal impressed upon the input of the amplifier when the resistance bulb indicates an increase in tem erature is 180 out of phase with that impressed upon the amplifier when the resistance bulb indicates a decrease in temperature.

In the same manner as that previously discussed, a signal potential is impressed upon amplifier I! by conductor Ill and ground connections 9|! and 9|, but this signal results in the appearance of an output potential between terminals 94 and 93 of the amplifier. This potential is conducted to winding III of relay ll through ground connections SI and III and conductor Ill is energizing relay I! to complete a circuit providing alternating current to motor II as follows: conductors Ill, III, and I". circuit controlling member 90, conductor III. motor I5, ground connections I00 and IIII, and back to conductor III. Completion of this circuit energizes motor II to rotate in such a direction as to close dampers 21 and II, and to move contact I! to the left along resistor II. This movement of contact I2 decreases B and increases 1) in the equation given above without changing the total resistance between terminal BII through resistor II to terminal 8|. Thus, although the current through B remains the same. 13 itself decreases until the voltage drop through B is the same as that through A. When this condition prevails. contacts 'II and I! are again at the same potential. no signal is impressed upon the input of the amplifier. and operation of the motor is interrupted.

This rotation of motor I5. however, has at the same time rotated dampers 21 and II into more nearly closed positions and the air flow through the burner portion of the heater means is restricted, reducing the supply of combustible vapor to the burner. If the increase in temperature is of suihcient magnitude, as for example. if the craft emerges into an atmosphere of relatively higher temperature, the change in resistance of bulb I0 may be so great that in order to produce a balancing change in resistance of resistor I1. motor I5 causes contact I2 to move to the left through its full stroke, simultaneously entirely closing dampers 21 and 3|. It will be understood that conventional limit switches, not shown, are provided on the shaft of motor IE to interrupt energization of the motor as it approaches extreme positions before damage is done to the instrument. It will also be understood that closing of damper 34 interrupts the supply of combustible vapor through the burner, whose flame is therefore extinguished.

Suppose now that the craft of which airfoil II comprises a part performs a maneuver which greatly increases its airspeed: for instance, suppose it goes into a power dive. The flow of air through conduit 22 immediately becomes large and produces a pressure diflerential between the combustion chamber and the conduit suflicient to cause arm 44 to make electrical contact with contact 50. The effect of this is to short circuit resistance B I, thus producing a large decrease in the resistance A, which results in the appearance of a large unbalance signal upon input terminals 88 and 81. This signal is of the same phase as that impressed thereon by increase in the resistance of resistor Ill due to rise in temperature. and results in an output signal across terminals 9| and 83 of amplifier I3 which energizes relay 81 through conductor III and ground connections III! and 95. Energization of relay 8! is efl'ective to provide electrical energy to motor I! through a circuit which may be traced as follows: conductors I03, H6. and I22, circuit closing member 99, conductor I23, motor I5, ground connections I08 and I05, and back to conductor Ill. Motor I5 is thus energized to rotate in a direction to close dampers 21 and 34 and at the same time moves contact arm I2 to the left as shown in the figure to decrease resistance B and increase D. However, the size of resistor BI is so selected that for any value of resistance of the bulb I0, the bridge cannot be balanced within the possible range of movement of contact 12, so that motor it rotates until it opens a limit switch, not shown,

9 contact I! being near the left end of resistor i1.

While the abnormal air speed continues, the resistance of bulb Ill may still change in either direction, depending on the atmospheric conditions through which the craft is diving. When the craft levels out. the pressure diflerential decreases so that arm N no longer makes contact with contact iii. resistor 6| is again included in resistance A, and the position of contact 12 at the left end of resistor ll results in a large unbalance of the bridge in the direction opposite to that previously described, unless the craft has descended into such a warm atmosphere that resistance C is great compared to resistance A. In any case, the circuit operates as detailed above to bring about a state of affairs in which A/C=B/D, when the dampers if and M are in a position regulating the supply of heat to the airfoil in accordance with the temperature at bulb Hi.

It will be apparent that a decrease in pressure differential suflicient to cause arm 44 to come into contact with contact ll has the same effect on the bridge circuit and therefore upon the operation of motor I as the increase in pressure differential just described.

In the direction of the system I have Just set forth, it will be seen that arm 44 and contacts 50 and Ii comprise a pair of normall open switches connected in parallel. and that variation in the pressure acts to close one of these switches depending upon whether the variation is due to excessively large or excessively small pressure diii'erential. Since under certain conditions it is desirable to use a normally closed switch rather than a normally open switch. I show in Figure 2 a switch suitable for such use.

It will be noted that arm I is provided with an insulated portion I on that side of pivot ill remote from the pressure responsive members. A pair of arms Ill and Ill bearing respectively contact members II! and III are normally spring urged toward one another so that members I52 and I53 make electrical contact. Portion N9 of arm I projects between arms I" and III, but does not touch either, if the pressure differential is within the selected range. However, if arm I is rotated in response to variation in the pressure differential in a counter-clockwise direction, insulated member I49 contacts arm ill and moves it away from arm llll. Stops iii and I" are provided so that substantial motion of either of the arms toward the other beyond a position corresponding to contact between members I52 and I" is prevented: therefore. movement or arm III in response to pressure by portion I of arm I is effective to open the electrical circuit between contacts ii! and I". Arm IE0 is connected to input terminal I" of bridge 2i! by conductor Ill and arm III is connected to the electrical connection I" between resistors I62 and if" as by conductor I51. In the normal condition of the switch, resistor I62 is shorted out of the bridge, the size of whose resistors are selected to be appropriate to this modified construction. If the electrical connection between contacts III and III is for any reason interrupted, this short circuit is broken and a resistance of the value of resistor 82 is inserted into the upper right hand arm of the bridge. As is well known to those familiar with the Wheatstone bridge, the insertion of added resistance in the upper right hand arm of the bridge has the same eil'ect on the bridge as the shorting out of an equivalent resistance in the 10 upper left hand arm of the bridge. Therefore. the system functions as clearly described in connectlon with Figure 1.

In the foregoing specification I have completely disclosed a system for heating airfoil surfaces to prevent the accretion of ice thereon. and for removing any accretion of ice inadvertently allowed to form. My system includes improvements and features of novelty particularly relating to the regulation of this system to Perform its function under normal conditions, and also safety means for overriding normal control of my system in the event of abnormal conditions of operation. Since minor changes and equivalent expedients may occur to those skilled in the art after a study of the specification, I therefore wish this disclosure to be considered as illustrative only, and to be limited only by the following claims.

I claim as my invention:

1. In a device of the class described, in combinatlon, a hollow airfoil surface having a leading edge, a fuel burner in heat transfer relation with said surface in the region of said edge. and normally ineffective air pressure responsive means for responsively causing restriction of the supply of fuel to said burner in the event of limiting air pressure conditions.

2. In a device of the class described, in combination, a hollow airfoil surface having a leading edge. a fuel burner in heat transfer relation with said airfoil surface in the region of said leading edge, means for supplying a combustible mixture of fuel and air to said burner, and normally ineffective air pressure responsive means for responsively causing restriction of said supply of combustible mixture in the event of limiting air pressure conditions.

3. In a device of the class described, in combination. a hollow airfoil surface having a leading edge, a fuel burner in heat transfer relation with said airfoil surface in the region of said leading edge, means for supplying a combustible mixture of fuel and air to said burner, air pressure responsive means for responsively causing restriction of said supply of combustible mixture, and temperature responsive means for independently causing restriction of said supply of combustible mixture.

4. In a device of the class described, in combination. a hollow airfoil surface having a leading edge, heater means in heat transfer relation with said airfoil surface in the region of said leading edge, said heater means comprising a first conduit for air to be heated, and a second conduit including a combustion chamber, means adapted to conduct fuel to said chamber, and Venturi means for causing flow of air and of said fuel in a combustible mixture into said combustion chamber. means for supplying air to said conduits, and air pressure responsive means for responsively causing restriction of the flow of said air through said conduits.

5. In a device of the class described. in combination, a hollow airfoil surface having a leading edge, heater means in heat transfer relation with said airfoil surface in the region of said leading edge. said heater means comprising first conduit means for air to be heated and second conduit means including a combustion chamber, means adapted to conduct fuel to said chamber, and Venturi means for causing flow of air and of said fuel in a combustible mixture into said combustion chamber, means providing a flow of air through said conduits in magnitude proportional 11 to the velocity of said surface in moving through the atmosphere, and means for causing restriction of the flow of said air through said conduits on excessive departure of the magnitude of said air flow from a predetermined value.

6. In a device of the class described, in combination, a hollow airfoil surface having a leading edge, heater means in heat transfer relation with said airfoil surface in the region of said leading edge. said heater means comprising first conduit means for air to be heated and second conduit means including a combustion chamber, means adapted to conduct fuel to said chamber, and Venturi means for causing flow of air and of said fuel in a combustible mixture into said combustion chamber, means providing a flow of air through said conduits in magnitude proportional to the velocity of said surface in moving through the atmosphere, means for restricting the flow of air through said conduits, means electrically responsive to the temperature of said airfoil surface, means electrically responsive to the magnitude of said air flow, and motor means actuating said restricting means under the influence of said responsive means, whereb to restrict said flow of air independently on excessive rise of the temperature of said surface and on excessive departure of the magnitude of said flow from a predetermined value.

'1. In an aircraft deicing system, a. hollow airfoil surface, heater means including a burner in convective heat transfer relation with said airfoil surface, enturi means for supplying fuel to said burner. means directing air through said Venturi means at a velocity determined by the speed of said surface in moving through the atmosphere, and means, responsive to the velocity of said air, for causing restriction of the flow of said air on excessive departure of said velocity from a predetermined value.

8. In a device of the class described, in combination, a hollow airfoil surface, first means delivering air within said airfoil surface, heater means for raising the temperature of said air, said heater means comprising means adapted to conduct liquid fuel to said heater means and Venturi means adapted to atomizingly dispense said fuel from said first means, second means delivering air to said Venturi means, third means conducting products of combustion from said heater means, restricting means in said last mentioned means, means in said first mentioned means for restricting the flow of air having passed through said heater means, temperature responmeans actuating said restricting means, electric circuit interrupting means actuated by the difference in pressure between said second means and said third means, and means operatively associating said motor, said temperature responsive means and said pressure responsive means whereby each of said last mentioned means may independently influence the operation of said motor.

9. In a device of the class described, in combination, a hollow airfoil surface having a leading edge and a trailing edge, heater means, first means conducting air to said heat exchanger, second means delivering air from said heater means to the interior of said airfoil surface in the region of said leading edge, said heater means including a burner, third means adapted to supply liquid fuel to said burner, fourth means for pneumatically causing flow of fluid from said supply means in the form of an atomized spray, said first means further conducting air to said fourth means, fifth means conducting products of combustion from 12 said heater means, sixth means restricting the flow of air through said second means, seventh means restricting the flow of air through said fifth means, motor means actuating said restricting means, ninth means electrically responsive to the temperature of said airfoil surface, tenth means operatively associatingsaid temperature responsive means and said motor means, eleventh means mechanically responding to the pressure differential between said first means and said first means, electric circuit interrupting means actuated by said eleventh means, and means electrically associating said interrupting means with said ninth means, whereby operation of said motor means may be influenced independently by said ninth means and said interrupting means.

10. In a device of the class described, in combination, an aircraft member having a portion to be heated, a fuel burner in heat transfer relation with said member in the region of said portion, means supplying air to said burner at a rate depending upon the air speed of said aircraft, and normally ineffective means responsive to said air speed for limiting the heat output of said burner under conditions of either excessively low or excessively high air speed.

11. In a device of the class described, in combination, a hollow airfoil surface having a leading edge, a fuel burner in heat transfer relation with said surface in the region of said edge, means supplying air to said burner at a rate depending upon the speed of said surface with re spect to the air, and normally ineffective means responsive to said speed for limiting the heat output of said burner under adverse conditions.

12. In a device of the class described, in combination, a hollow airfoil surface having a leading edge, heater means in heat transfer relation with said airfoil surface in the region of said leading edge, said heater means comprising a first conduit for air to be heated, and a second conduit including a combustion chamber, means adapted to conduct fuel to said chamber, means supplying air to said combustion chamber at a rate depending upon the speed of said airfoil through the air, and means responsive to said speed of said airfoil for causing restriction or the flow of said air.

13. In a device of the class described, in combination, a hollow airfoil surface having a leading edge, heater means in heat transfer relation with said airfoil surface in the region of said leading edge, said heater means comprising first conduit means for air to be heated and second conduit means including a combustion chamber, means adapted to conduct fuel to said chamber, means supplying air to said combustion chamber at a rate depending upon the speed of said airfoil through the air, and means responsive to said speed of said airfoil for causing restriction of the flow of said air.

14. In a device of the class described, in combination, an aircraft member having a portion to be heated, heater means in heat transfer relation with said aircraft member in the region of said portion, said heater means comprising first conduit means for air to be heated and second conduit means including a combustion chamber, means adapted to conduct fuel to said chamber, and Venturl means for causing flow of air and of said fuel in a combustible mixture into said combustion chamber, means providing a flow of air through said conduits in magnitude proportional to the velocity of said surface in moving through the atmosphere, means for restricting the flow of air through said conduits. means electrically responsive to the temperature of said aircraft member, means electrically responsive to the magnitude of said air flow, and motor means actuating said restricting means under the influence 01' said responsive means, whereby to restrict said flow of air independently on excessive rise of the temperature of said surface and on excessive departure of the magnitude of said flow from a predetermined value.

15. In apparatus for controlling heater means for a vehicle wherein the operation of the heater means is dependent on the rate of air flow through said means, in combination, conduit means for conducting air through said heater means, means for controlling air flow through said conduit, and normally ineffective means responsive to the rate or air flow through said conduit for regulating said controlling means in a manner to limit the maximum rate of air flow through said conduit to a predetermined value.

16. In apparatus for controlling heater means for a vehicle wherein the operation of the heater means is dependent on the rate of air flow 14 through said means, in combination, conduit means for conducting air through said heater means, means for controlling air flow through said conduit, and normally ineflective means responsive to the rate of air flow through said conduit for regulating said controlling means in a manner to limit the minimum rate of air flow through said conduit to a predetermined value. WILLIAM J. FIELD.

REFERENCES CITED The following references are oi record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,272 Price Feb, 16, 1943 2,022,959 Gordon Dec. 3, 1935 2,063,477 Young et a1. Dec. 8, 1936 2,262,003 Hoffman et a1 Nov. 11. 1941 2,314,089 Hess et a1 Mar. 16, 1943 2,321,940 Robertson June 15, 1943 2,337,484 McCollum Dec. 21. 1.943 2,364,458 McCoilum Dec. 5, 1944 Certificate of Correction Patent No. 2,437,318.

March 9, 1948.

WILLIAM J. FIELD It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 9, line 27, for direction read description; column 11, line 54, claim 8, after the syllable and hyphen respon-" insert sive means within said airfoil surface, motor; co

umn 12, line 11, for first read fifth; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of October, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uommian'oner of Patents.

the flow of air through said conduits. means electrically responsive to the temperature of said aircraft member, means electrically responsive to the magnitude of said air flow, and motor means actuating said restricting means under the influence 01' said responsive means, whereby to restrict said flow of air independently on excessive rise of the temperature of said surface and on excessive departure of the magnitude of said flow from a predetermined value.

15. In apparatus for controlling heater means for a vehicle wherein the operation of the heater means is dependent on the rate of air flow through said means, in combination, conduit means for conducting air through said heater means, means for controlling air flow through said conduit, and normally ineffective means responsive to the rate or air flow through said conduit for regulating said controlling means in a manner to limit the maximum rate of air flow through said conduit to a predetermined value.

16. In apparatus for controlling heater means for a vehicle wherein the operation of the heater means is dependent on the rate of air flow 14 through said means, in combination, conduit means for conducting air through said heater means, means for controlling air flow through said conduit, and normally ineflective means responsive to the rate of air flow through said conduit for regulating said controlling means in a manner to limit the minimum rate of air flow through said conduit to a predetermined value. WILLIAM J. FIELD.

REFERENCES CITED The following references are oi record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,272 Price Feb, 16, 1943 2,022,959 Gordon Dec. 3, 1935 2,063,477 Young et a1. Dec. 8, 1936 2,262,003 Hoffman et a1 Nov. 11. 1941 2,314,089 Hess et a1 Mar. 16, 1943 2,321,940 Robertson June 15, 1943 2,337,484 McCollum Dec. 21. 1.943 2,364,458 McCoilum Dec. 5, 1944 Certificate of Correction Patent No. 2,437,318.

March 9, 1948.

WILLIAM J. FIELD It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 9, line 27, for direction read description; column 11, line 54, claim 8, after the syllable and hyphen respon-" insert sive means within said airfoil surface, motor; co

umn 12, line 11, for first read fifth; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of October, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uommian'oner of Patents. 

